SEA-FISHERIES LABORATORY. 275 



HYDROGRAPHIC INVESTIGATIONS AND THE 

 FISHERIES OF THE IRISH SEA. 



By Jas. Johnstone, B.Sc. 



(With Charts.) 



The variations of the salinity of the water of the 

 Irish Sea, during the year 1912, are discussed by 

 Dr. Bassett in another paper in this Report; and the 

 relation of these salinity variations to the general circula- 

 tion of water in this area, and to the weather of the 

 year are also considered. The present paper deals with 

 the temperature observations only, and an attempt is 

 made to correlate these data with the fluctuations in the 

 winter plaice fishery off the coast of North Wales. This 

 attempt has not proved to be a very successful one ; never- 

 theless, it seems to be useful to attempt to discover what 

 results may be obtained from the data available. 



I. The Temperature Observations. These are : — 



(1). Semi-diurnal sea-temperatures, at the surface, 

 at various Irish Sea Light "Vessels. These observations 

 are made for the Meteorological Office, and copies have 

 kindly been supplied to us. The temperatures of the sea 

 at 4 p.m. are abstracted, 10-daily and monthly means 

 being calculated. The monthly means are given in 

 Table I. 



(2). Hourly temperature observations made by the 

 officers of the S.S. James Fletcher, when at sea doing 

 scientific work and police duty. These observations 

 are carefully made, and are very numerous, Neverthe- 

 less, the cruises of the ship are necessarily restricted to 

 certain lines and areas, and the variable nature of the 



